WASHINGTON � President Barack Obama will Thursday extend a moratorium on new deepwater drilling for six months, and unveil a major curtailment of the offshore oil industry, after a review of the Gulf disaster.

The president will also announce that planned exploration off the Alaska coast in the Chukchi and Beaufort seas will be delayed pending a presidential commission into deepwater offshore drilling, a White House aide said.

In addition, a planned August lease sale of drilling rights in the Western Gulf will be cancelled and a lease sale off the coast of Virginia will also be scotched, due to environmental concerns and Defense Department input.

The aide, speaking on condition of anonymity, said that Obama would also announce standards to "strengthen oversight of the industry and enhance safety," pending the recommendations of the presidential commission.

Obama, who will formally announce the steps in a White House press conference later Thursday, was briefed on the initial report into the disaster by Interior Secretary Ken Salazar in the Oval Office on Wednesday night.

The president will announce the new restrictions on the industry as BP presses ahead with a "top kill" operation designed to finally plug the ruptured well that is gushing oil into the Gulf of Mexico in an environmental disaster.

"While the Commission performs its work to determine how to prevent this from ever happening again, the moratorium on permits to drill new deepwater wells will continue for a period of six months," the aide said.

The measures represent a partial reversal of a controversial Obama plan to expand offshore oil drilling announced at the end of March, which angered green groups and spurred charges by Republicans that it did not go far enough.

The president's plan, part of a comprehensive energy strategy, was to have seen new tracts of the Atlantic off the Virginia coast opened to exploration, and expanded prospecting leases in the Gulf off the coast of Florida.

Scientific research in the Chukchi and Beaufort seas was also to be authorized.

"In the short term, as we transition to cleaner energy sources, we'll have to make tough decisions about opening new offshore areas for oil and gas development in ways that protect communities and coastlines," Obama said in March.

He portrayed the decision as part of a comprehensive energy plan, designed to wean the United States off foreign energy sources from volatile areas, and develop a new green economy.

The measures were seen by some observers at the time as a political move, designed to win some Republican support for a comprehensive climate change and energy bill in the Senate.

Republicans, who have marched in lock step to oppose almost all of Obama's domestic agenda, backed wider exploration of untapped US reserves, and adopted a "Drill, baby, drill," mantra during the 2008 presidential campaign.

The measures unveiled in March reversed a campaign pledge Obama made in 2008, when he said that the amount of time it would take to produce large amounts of offshore oil did not justify the risks of extracting it.